Internal combustion engine intake pressure detecting device

ABSTRACT

An internal combustion engine ( 18 ) has an intake pipe ( 34 ) which extends from an internal combustion engine main body ( 19 ) and an intake passageway ( 33 ) formed in the interior thereof communicates with an intake passageway ( 27 ) formed in the internal combustion engine main body ( 19 ), a fuel supply means ( 36 ) for supplying fuel to the internal combustion engine main body ( 19 ), an intake negative pressure sensor ( 43 ) for detecting an intake negative pressure (P) in the intake passageway ( 33 ) within the intake pipe ( 34 ), and a control unit ( 44 ) for controlling the supply of fuel to the internal combustion engine main body ( 19 ) by the fuel supply means ( 36 ) based on a detection signal of the intake negative pressure sensor ( 43 ). The intake negative pressure sensor ( 43 ) is adapted to detect an intake negative pressure at a downstream end ( 42 ) of the intake passageway ( 33 ) within the intake pipe ( 34 ). According the intake negative pressure sensor ( 43 ), the value of the intake negative pressure (P) in the intake passageway ( 27 ) in the internal combustion engine main body ( 19 ) is detected accurately.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to an intake negative pressure detectingdevice for an internal combustion engine which is designed to detectintake negative pressure inside an intake passageway within an intakepipe.

2. Background Art

There exists conventional intake negative pressure detecting devices forinternal combustion engines.

A coventional internal combustion engine includes an intake pipe whichextends from an internal combustion engine main body having a cylinderand a piston and in which an intake passageway formed in the interiorthereof communicates with an intake passageway formed in the internalcombustion engine main body. A fuel supply unit supplies fuel to theinternal combustion engine main body. An intake negative pressure sensorfor detecting the intake negative pressure in the intake passagewaywithin the intake pipe and a control unit for controlling the supply offuel to the internal combustion engine by the fuel supply unit based ona detection signal of the intake negative pressure sensor are alsoprovided.

When the internal combustion engine is in operation, the intake negativepressure in the intake passageway is detected by the intake negativepressure sensor, and a detection signal of the sensor is then inputtedinto the control unit. Then, the fuel supply unit is controlled by thecontrol unit, so that an amount of fuel that matches the intake negativepressure so detected is supplied to the internal combustion engine mainbody by the fuel supply unit.

According to the control of the fuel supply unit by the control unit,the fuel consumption of the internal combustion engine is improved, andinclusion of harmful substances contained in exhaust emissions issuppressed.

Incidentally, a detecting position of the intake negative pressure bythe intake negative pressure sensor is situated upstream from the fuelsupply unit and is far apart from the internal combustion engine mainbody.

Due to this, an error tends to be easily produced between a detectedvalue of the intake negative pressure by the intake negative pressuresensor and a value of the intake negative pressure in the intakepassageway in the internal combustion engine main body that results whenthe detection is carried out by the intake negative pressure sensor. Asa result, there is caused a risk that an amount of fuel that matches theintake negative pressure in the intake passageway in the internalcombustion engine main body is not supplied. Namely, there still remainareas needing to be improved with respect to the improvement in fuelconsumption of the internal combustion engine and the prevention ofemission of harmful substances.

SUMMARY OF THE INVENTION

The invention was made in view of the above situations, and an advantagethereof is to realize a more accurate detection of an intake negativepressure value in an intake passageway in an internal combustion enginemain body so as to improve the fuel consumption of an internalcombustion engine and to reduce harmful substances contained in exhaustemissions through a control based on the value thus detected.

In addition, another advantage of the invention is to attain the aboveadvantage with a simple construction.

According to an aspect of the invention, there is provided an intakenegative pressure detecting device for an internal combustion engineincluding an intake pipe which extends from an internal combustionengine main body and an intake passageway formed in the interior thereofcommunicates with an intake passageway formed in the internal combustionengine main body. A fuel supply unit supplies fuel to the internalcombustion engine main body, an intake negative pressure sensor detectsan intake negative pressure in the intake passageway within the intakepipe, and a control unit controls the supply of fuel to the internalcombustion engine main body by the fuel supply unit based on a detectionsignal of the intake negative pressure sensor. The intake negativepressure detecting device provides that the intake negative pressuresensor is adapted to detect an intake negative pressure at a downstreamend of the intake passageway within the intake pipe.

According to the aspect of the invention, since an intake negativepressure at the downstream end of the intake pipe which is situated inthe vicinity of the intake passageway in the internal combustion engineman body is detected by the intake negative pressure sensor, the intakenegative pressure sensor can detect more accurately the intake negativepressure value in the intake passageway in the internal combustionengine main body.

Consequently, the fuel supply unit is controlled by the control unitbased on the detection signal of the intake negative pressure sensorsuch that an appropriate amount of fuel is supplied to the internalcombustion engine main body by the fuel supply unit, and therefore, thefuel consumption of the internal combustion engine is improved, andharmful substances contained in exhaust emissions are reduced.

In addition, the intake negative pressure sensor is mounted directly onan exterior side of the intake pipe and a communication passageway isformed in the intake pipe for causing the intake passageway in theintake pipe to communicate with the intake negative pressure sensor.

Incidentally, the cross-sectional area of a downstream sidecommunication passageway which constitutes a portion of thecommunication passageway which is situated on the intake negativepressure sensor side may be made larger than the cross-sectional area ofan upstream side communication passageway which constitutes a portion ofthe communication passageway which is situated on the intake passagewayside. The intake negative pressure sensor may include a housing whichconstitutes an outer shell thereof and which is mounted on an exteriorside of the intake pipe and a sensor main body accommodated in theinterior of the housing for detecting an intake negative pressure, and apressure transmitting passageway is formed in the housing fortransmitting an intake negative pressure from the downstream sidecommunication passageway to the sensor main body side. An opening of thepressure transmitting passageway which opens to the interior of thedownstream side communication passageway may be deviated from the centerof an opening of the upstream side communication passageway which opensto the interior of the downstream side communication passageway in adirection normal to the center of the opening.

In addition, the intake pipe may be formed so as to be curved into anarc-like shape substantially about an imaginary point, and an opening ofthe communication passageway which is situated at an end portion on theintake passageway side thereof may be positioned in a portion on aninner circumferential surface of the intake pipe which is closer to theimaginary point at the downstream end of the intake passageway.

According to another aspect of the invention, ther is provided an intakenegative preessure detecting device for an internal combustion engingecomprising an intake passageway communicating with a combustion chamber(25), a fuel supply means (36) for supplying fuel to the combustionchamber (25), an intake negative pressure sensor (43) for detecting anintake negative pressure (P) in the intake passageway through acommunication passageway (47), and a control unit (44) for controllingthe supply of fuel by the fuel supply means (36) based on a detectionsignal of the intake negative pressure sensor (43), the intake negativepressure detecting device for an internal combustion engine beingcharacterized in that the intake passageway is extended upwardly fromthe combustion chamber (25), the intake passageway is curvedly formed soas to be curved as it extends upwardly into an arc-like shapesubstantially about an imaginary point (65), one end portion of thecommunication passageway (47) is opened to a curved portion of theintake passageway, the communication passageway (47) is extendedupwardly from the one end portion, and another end portion of thecommunication passageway (47) is opened to the intake negative pressuresensor (43) side.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially enlarged cross-sectional view of FIG. 2,

FIG. 2 is an overall side view of a vehicle,

FIG. 3 is a partially enlarged cross-sectional view of FIG. 1, and

FIG. 4 is a graph showing operating conditions of an internal combustionengine.

DETAILED DESCRIPTION OF THE INVENTION

The invention will be described in more detail with reference to theaccompanying drawings.

In the drawings, reference numeral 1 denotes a vehicle illustrated inthe form of a straddle type motorcycle, and an arrow Fr indicates aforward direction of the vehicle 1.

A vehicle body 2 of the vehicle 1 includes a vehicle main body 3 whichis mainly made up of a vehicle body frame, a front fork 4 supported at afront end portion of the vehicle main body 3 in such a manner as to besteered freely, a front wheel 5 rotationally supported at a lower endportion of the front fork 4, and a handlebar 6 supported at an upper endportion of the front fork 4. The vehicle body 2 also includes a rear arm8 disposed to the rear of a lower portion of the vehicle main body 3 soas to extend longitudinally and pivotally supported at a front endportion thereof by a pivot shaft 7 at a rear lower portion of thevehicle main body 3 so that a rear portion of the rear arm 8 is allowedto swing vertically. A rear wheel 9 is rotationally supported at a rearend portion of the rear arm 8 and a shock absorber 10 for allowing therear portion of the rear arm 8 to be resiliently supported on a rearupper portion of the vehicle main body 3. The vehicle body 2 issupported on a road surface 11 by the front and rear wheels.

The vehicle 1 includes a seat 14 supported on an upper surface of therear upper portion of the vehicle main body 3 and an articleinstallation space 15 for installing a small article such as a helmetwhich is situated above the rear wheel 9 and below the seat 14 andformed in the interior of the rear upper portion of the vehicle mainbody 3 in such a manner as to open upwardly. The seat 14 opens andcloses the upper surface of the rear upper portion of the vehicle mainbody 3, and the article installation space 15 is allowed to openupwardly when the seat 14 is so operated, whereby a small article suchas a helmet can be taken out of or placed in the article installationspace 15.

The vehicle 1 includes a four-cycle internal combustion engine 18 whichis mounted on the vehicle main body 3 and which constitutes a drivingsource for the vehicle 1 when running. The internal combustion engine 18has an internal combustion engine main body 19 which constitutes a frontportion of the rear arm 8. The internal combustion engine main body 19includes a crankcase 20 which is pivotally supported on the vehicle mainbody 3 by the pivot shaft 7, a cylinder 21 which protrudes forward fromthe crankcase 20, a piston 22 which is fitted in the cylinder 21, and aconnecting rod 23 for allowing a crankshaft rotationally supported onthe crankcase 20 to interlock with and connect to the piston 22. A spacein the cylinder 21 which is defined by a cylinder head 24 whichconstitutes a protruding end portion of the cylinder 21 and the piston22 is made to constitute a combustion chamber 25.

An intake passageway 27 is formed in the cylinder head 24 of thecylinder 21 which extends from a top portion of the cylinder head 24 tocommunicate with the combustion chamber 25. This intake passageway 27extends downwardly from an upper end opening thereof to open to thecombustion chamber 25, and an intake valve 28 is supported on thecylinder head 24 in such a manner as to open and close the opening ofthe intake passageway 27 directed toward the combustion chamber 25. Inaddition, an exhaust passageway 30 is formed in the cylinder head 24which provides a communication from the combustion chamber 25 to belowthe cylinder head, and an exhaust valve 31 is supported on the cylinderhead 24 in such a manner as to open and close the exhaust passageway 30.The intake valve 28 and the exhaust valve 30 are made to interlock withand connect to the crankshaft via a valve train, not shown, so as to beoperated to perform appropriate opening and closing actions.

The internal combustion engine 18 includes an intake pipe 34 whichextends upwardly from an upper surface side of the internal combustionengine main body 19 and in which an intake passageway 33 formed in theinterior thereof communicates with the intake passageway 27 formed inthe cylinder head 24 of the internal combustion engine main body 19. Athrottle valve 35 is interposed at an intermediate position along thelength of the intake pipe 34 and adapted to adjust the opening of theintake passageway 33 in the intake pipe 34. A fuel supply unit 36 whichmay be a fuel injection valve, for supplying fuel at a position upstreamof the throttle valve 35 to the combustion chamber 25 in the internalcombustion chamber main body 19 via the intake passageway 33 in theintake pipe 34. An air cleaner 37 is mounted on an extending end portionof the intake pipe 34. A fuel tank 38 for storing fuel that is to besupplied to the fuel supply unit 36 is disposed near the fuel supplyunit 36 in front thereof, and the fuel tank 38 is supported on thevehicle main body 3.

The rear arm 8 is made to be a swinging driving unit. Namely, the reararm 8 includes the internal combustion chamber main body 19 whichconstitutes a front part of the rear arm 8 and a power transmission 41which is provided in such a manner as to continue to a rear part of theinternal combustion engine main body 19 and which rotationally supportsthe rear wheel 9 to make the rear wheel 9 interlock with and connect tothe internal combustion engine main body 19.

The internal combustion engine includes a crank angle sensor 39 fordetecting a crank angle θ of the crankshaft in the internal combustionengine main body 19, a throttle position sensor 40 for detecting theopening of the intake passageway in the throttle valve 35 (throttleopening), an intake negative pressure sensor 43 for detecting an intakenegative pressure P at a downstream end 42 of the intake passageway 33in the intake pipe 34 and a control unit 44 for electronicallycontrolling the amount of fuel injected by the fuel supply unit 36 forsupply to the combustion chamber 25 in the internal combustion enginemain body 19 based on detection signals from the respective sensors 39,40, 43.

The intake negative pressure sensor 43 is detachably fastened to anexterior side of a downstream end portion of the intake pipe 34 whichcorresponds to the downstream end 42 of the intake passageway 33 in theintake pipe 34 with a fastener 46, whereby the intake negative pressuresensor 43 is mounted directly on the exterior side of the intake pipe34. A communication passageway 47 is formed in the downstream endportion of the intake pipe 34 for providing a communication between thedownstream end 42 of the intake passageway 33 in the intake pipe 34 andthe intake negative pressure sensor 43.

In the communication passageway 47, the cross-sectional area S2 of adownstream side communication passageway 49 which constitutes a portionof the communication passageway which is situated on the intake negativepressure sensor 43 side is made larger than the cross-sectional area S1of an upstream side communication passageway 48 which constitutes aportion of the communication passageway which is situated on the intakepassageway side. That is, the volume of the downstream sidecommunication passageway is made to be a large volume air chamber. Theupstream side communication passageway 48 extends linearly from thedownstream end 42 side of the intake passageway 33 toward the downstreamside communication passageway 49 side and is formed into a shape whosehorizontal cross section remains the same sized circle alongsubstantially the full length thereof.

The intake negative pressure sensor 43 includes a housing 51 whichconstitutes an outer shell of the intake negative pressure sensor 43 andwhich is mounted directly on an exterior side of the intake pipe 34 viaa packing or the like, and a sensor main body 52 which is a sensor suchas a strain sensor accommodated in the interior of the housing 51 fordetecting an intake negative pressure P at the downstream end 42 of theintake passageway 33.

The housing 51 includes a housing main body 53 for accommodating thesensor main body 52 in the interior thereof and a pressure transmittingpipe 54 extending linearly from the housing main body 53 toward theinterior of the downstream side communication passageway 49. A pressuretransmitting passageway 55 is formed in the interior of the pressuretransmitting pipe 54 in such a manner as to provide a communication fromthe downstream side communication passageway 49 toward the sensor mainbody 52 side for transmitting an intake negative pressure P from thedownstream side communication passageway 49 to the sensor main body 52.The pressure transmitting passageway 55 is formed into a shape whosehorizontal cross section remains the same seized circle alongsubstantially the full length thereof.

An opening 59 of the pressure transmitting passageway 55 which is madeto face the interior of the downstream side communication passageway 49is deviated relative to a center 58 of an opening 57 of the upstreamside communication passageway 48 which is made to face the interior ofthe downstream side communication passageway 49 in a direction normal tothe center 58.

When the internal combustion engine 18 is in operation, in associationwith the operation of the internal combustion engine main body 19,atmospheric side air 62 is sucked into the combustion chamber 25 afterhaving passed sequentially through the air cleaner 37, the fuel supplyunit 36 and the respective intake passageways 27, 33 in that order. Asthis occurs, fuel is supplied into the intake passageway 33 by the fuelsupply unit 36 so as to produce an air-fuel mixture. The air-fuelmixture so produced is then caused to flow into the combustion chamber25 for use in combustion, whereby a driving force is outputted from theinternal combustion engine main body 19 of the internal combustionengine 18. Combustion gases produced as a result of such combustion passthrough the exhaust passageway 30 and is then discharged to the outsideof the internal combustion engine 18 as exhaust emissions. Then, thedriving force so outputted is transmitted to the rear wheel 9 via thepower transmission 41, whereby the vehicle 1 is allowed to run on theroad surface 11.

In FIG. 4, the fuel injection timing (crank angle θ) and time period Tof injection A, that is, the injection amount of the fuel supply unit 36is designed to be determined based on detection signals of therespective sensors 39, 40, 43 by the fuel supply unit 36.

Namely, the timing of injection A by the fuel supply unit 36 isdetermined to take place at predetermined crank angles θ which aresubstantially identical to each other at transition timings from acompression stroke to a suction stroke of the internal combustion engine18, whereby each injection A is implemented, and the time period T ofinjection A is controlled as below. Namely, the time period T ofinjection A of fuel is determined in accordance with the magnitude of anintake negative pressure P detected by the intake negative pressuresensor 43 at predetermined crank angles θ1 which are substantiallyidentical to each other at transition timings from a compression stroketo a power stroke (which are regarded as identical to each other). Notethat in FIG. 4, P1 to P6 and A1 to A6 correspond to each other,respectively.

To be more specific, that the intake negative pressure P is large likeP1, P2 (or small like P3 to P6) means that the throttle position sensor40 detects the throttle opening as being closed (or open), requiring theoutput of less (or more) driving force. Due to this, the time period Tof injection A of fuel is made to be shorter like a time period T1 forinjections A1, A2 (or made to be longer like a time period of T2 forinjections A3 to A6).

In addition, whether or not the internal combustion engine 18 isoperated for acceleration is determined as below.

Namely, an intake negative pressure P is detected by the intake negativepressure sensor 43 in the aforesaid manner at predetermined crank anglesθ2 which are substantially identical to each other at transition timingsfrom an exhaust stroke to a suction stroke (which are regarded asidentical to each other), and it is designed such that when a differenceΔP=P8−P7 between intake negative pressures P7, P8 which are adjacent toeach other in terms of a time exceeding a predetermined set value, theinternal combustion engine 18 is determined as being operated foracceleration. Then, the time period T of injection A is set based on thedetermination.

The fuel consumption of the internal combustion engine 18 is improvedand the containment of harmful substances in constituents of exhaustemissions 63 is suppressed by controlling the fuel supply unit 36 by thecontrol unit 44.

According to the construction that has been described heretofore, theintake negative pressure sensor 43 is designed to detect an intakenegative pressure P at the downstream end 42 of the intake passageway 33in the intake pipe 34.

Due to this, since the intake negative pressure P at the downstream end42 of the intake pipe 34 which is located in the vicinity of the intakepassageway 27 in the internal combustion engine main body 19 is detectedby the intake negative pressure sensor 43, according to this intakenegative pressure sensor 43, the value of an intake negative pressure Pin the intake passageway 27 in the internal combustion engine main body19 can be detected more accurately.

Consequently, according to the detection signal of the intake negativepressure sensor 43, the fuel supply unit 36 is controlled by the controlunit 44 such that the fuel supply unit 36 supplies an appropriate amountof fuel to the internal combustion engine main body 19, and owing tothis, the fuel consumption of the internal combustion engine 18 isimproved, and harmful substances in the exhaust emissions 63 arereduced.

In addition, as has been described above, the intake negative pressuresensor 43 is designed to detect the intake negative pressure P at thepredetermined crank angles θ1.

Due to this, in case a crank angle θ at which the intake negativepressure P at the downstream end 42 of the intake passageway 33 in theintake pipe 34 becomes a relatively large value is set as thepredetermined crank angle θ1, errors between values detected by theintake negative pressure sensor 43 can be reduced to a lower level.

Consequently, according to the detection signal from the intake negativepressure sensor 43, the fuel consumption of the internal combustionengine 18 is improved, and the harmful substances in the exhaustemissions 63 are reduced.

Additionally, the intake negative pressure sensor 43 is mounted directlyon the exterior side of the intake pipe 34, and the communicationpassageway 47 is formed in the intake pipe 34 for providing acommunication between the intake passageway 33 in the intake pipe 34 andthe intake negative pressure sensor 43.

Due to this, since the intake negative pressure P in the intake pipe 34at the intake passageway 33 is detected by the intake negative pressuresensor 43 more directly, the value of the intake negative pressure P inthe intake passageway 27 in the internal combustion engine main body 19can be detected more accurately by the intake negative pressure sensor43.

Consequently, the fuel supply unit 36 is controlled accordingly tosupply a more appropriate amount of fuel to the internal combustionengine main body 19, whereby the fuel consumption of the internalcombustion engine 18 is improved further and the harmful substances inthe exhaust emissions 63 are reduced further.

In addition, as has been described above, since the intake negativepressure sensor 43 is mounted directly on the exterior side of theintake pipe 34, the number of parts involved in the internal combustionengine 18 is reduced when compared with a case where the intake pipe 34and the sensor 43 are connected to each other via a tube, whereby theimprovement in fuel consumption and the like can be attained with asimple construction.

Additionally, as has been described before, in the internal combustionengine 18, the cross-sectional area S2 of a downstream sidecommunication passageway 49 which constitutes a portion of thecommunication passageway 47 which is situated on the intake negativepressure sensor 43 side is made larger than the cross-sectional area S1of an upstream side communication passageway 48 which constitutes aportion of the communication passageway 47 which is situated on theintake passageway side. The intake negative pressure sensor 43 includesthe housing 51 which is mounted directly on the exterior side of theintake pipe 34 and the sensor main body 52 which is accommodated in theinterior of the housing 51 for detecting the intake negative pressure P.The housing 51 includes the pressure transmitting passageway 55 fortransmitting the intake negative pressure P from the downstream sidecommunication passageway 49 to the sensor main body 52 side. The opening59 of the pressure transmitting passageway 55 which is made to face theinterior of the downstream side communication passageway 49 is deviatedrelative to the center 58 of the opening 57 of the upstream sidecommunication passageway 48 which is made to face the interior of thedownstream side communication passageway 49 in the direction normal tothe center 58.

Due to this, even in the event that some fuel which passes through theintake passageway 33 in the intake pipe 34 attempts to pass from theintake passageway 33 through the upstream side communication passageway48 and the downstream side communication passageway 49 sequentially tobe scattered toward the opening 59 of the pressure transmittingpassageway 55 of the intake negative pressure sensor 43, the fuel isrestrained from moving from the opening 57 of the upstream sidecommunication passageway 48 directly to the opening 59 of the pressuretransmitting passageway 55. Thus, the adhesion of fuel to the sensormain body 52 through the pressure transmitting passageway 55 of theintake negative pressure sensor 43 is prevented accordingly.

Thus, according to the intake negative pressure sensor 43, the value ofthe intake negative pressure P in the intake passageway 27 can bedetected more accurately without being interfered with by the fuel, sothat improvement of the fuel consumption of the internal combustionengine 18 can be surely achieved. Also, since the adhesion of fuel tothe sensor main body 52 of the intake negative pressure sensor 43 isprevented, the life duration of the intake negative pressure sensor 43is improved.

In FIGS. 1 and 3, as shown by double-dashed lines, the intake pipe 34 isformed to be curved into an arc-like shape toward the rear substantiallyabout the imaginary point 65 situated on the rear of the downstream endof the intake pipe 34. Then, an opening 66 of the communicationpassageway 47 situated at an intake passageway 33 side end portionthereof is positioned at a portion on the inner circumferential surfaceof the intake passageway 33 which is closer to the imaginary point 65 atthe downstream end 42 of the intake passageway 33 in the intake pipe 33.

Here, in the event that the intake pipe 34 is curved as described above,fuel flowing through the intake passageway 33 in the intake pipe 34toward the internal combustion engine main body 19 flows along a portionon the inner circumferential surface of the intake passageway 33 whichis farther apart from the imaginary point 65 by virtue of the inertiaforce thereof.

Due to this, as has been described above, in the event that the opening66 of the communication passageway 47 situated at the intake passageway33 side end portion thereof is positioned at the portion which is closerto the imaginary point 65 at the downstream end 42 of the intakepassageway 33 in the intake pipe 33, the easy entry of some of the fuelflowing through the intake passageway 33 in the intake pipe 34 into thecommunication passageway 47 is restrained, and the adhesion of fuelwhich flows in through the pressure transmitting passageway 55 of theintake negative pressure sensor 43 is prevented accordingly.

Consequently, according to the intake negative pressure sensor 43, theintake negative pressure P value in the intake passageway of theinternal combustion engine main body 19 is detected more accuratelywithout being interrupted by fuel, whereby the improvement in fuelconsumption of the internal combustion engine 18 and the like can beattained more accurately. In addition, the life of the intake negativepressure sensor 43 is extended as the adhesion of fuel to the sensormain body 52 of the intake negative pressure sensor 43 is restrained.

In this case, the opening 66 of the communication passageway 47 facingthe downstream end 42 of the intake passageway 33 in the intake pipe 34may be positioned at, among locations along the inner circumference ofthe intake passageway 33 at the downstream end 43 thereof, any locationalong a semi-circumference of the intake passageway 33 which are closerto the imaginary point 65.

In FIG. 3, as shown by the double-dashed lines, the fuel supply unit 36may be such as to inject fuel into the intake passageway 33 at aposition downstream of the throttle valve 35.

Note that while the description has been made by reference to theexample illustrated in the drawings, the internal combustion engine 18is not limited to such as one to be installed in the vehicle 1, and inaddition, the internal combustion engine 18 may be a 2-cycle one.Additionally, the fuel supply unit 36 may be a fuel injection valvewhich injects fuel directly into the cylinder 21 in the internalcombustion engine main body 19 or a carburetor.

In addition, the invention may be such as to be attained by combiningappropriately the aforesaid individual constituent members.

1. An intake negative pressure detecting device for an internalcombustion engine, comprising: an intake passageway extended upwardlyfrom the combustion chamber, the intake passageway being curvedly formedso as to be curved as it extends upwardly into an arc-like shapesubstantially about an imaginary point; and one end portion of acommunication passageway being opened to a curved portion of the intakepassageway, the communication passageway being extended upwardly fromthe one end portion, and another end portion of the communicationpassageway being opened to the intake negative pressure sensor side. 2.The intake negative pressure detecting device for an internal combustionengine as set forth in claim 1, wherein the intake pipe extends from aninternal combustion engine main body.
 3. The intake negative pressuredetecting device for an internal combustion engine as set forth in claim2, wherein the intake passageway is formed in the interior of the intakepipe and communicates with the intake passageway of the internalcombustion engine main body.
 4. The intake negative pressure detectingdevice for an internal combustion engine as set forth in claim 2,further comprising a fuel supply means for supplying fuel to theinternal combustion engine main body and a control unit that controlsthe supply of fuel to the internal combustion engine main body by thefuel supply means based on a detection signal of the intake pressuresensor.
 5. An intake negative pressure detecting device for an internalcombustion engine, comprising: an intake negative pressure sensoradapted to detect an intake negative pressure at a downstream end of theintake passageway within the intake pipe; and an intake pipe formed soas to be curved into an arc-like shape substantially about an imaginarypoint, and an opening of the communication passageway which is situatedat an end portion on the intake passageway side is positioned in aportion on an inner circumferential surface of the intake passagewaywhich is closer to the imaginary point at the downstream end of theintake passageway.
 6. The intake negative pressure detecting device foran internal combustion engine as set forth in claim 5, wherein theintake pipe extends from an internal combustion engine main body.
 7. Theintake negative pressure detecting device for an internal combustionengine as set forth in claim 6, wherein the intake passageway is formedin the interior of the intake pipe and communicates with the intakepassageway of the internal combustion engine main body.
 8. The intakenegative pressure detecting device for an internal combustion engine asset forth in claim 6, further comprising a fuel supply means forsupplying fuel to the internal combustion engine main body.
 9. Theintake negative pressure detecting device for an internal combustionengine as set forth in claim 8, further comprising a control unit thatcontrols the supply of fuel to the internal combustion engine main bodyby the fuel supply means based on a detection signal of the intakepressure sensor.
 10. An intake negative pressure detecting device for aninternal combustion engine, comprising: an intake negative pressuresensor adapted to detect an intake negative pressure at a downstream endof an intake passageway within an intake pipe wherein the intakenegative pressure sensor is mounted directly on an exterior side of theintake pipe; and a communication passageway formed in the intake pipefor causing the intake passageway in the intake pipe to communicate withthe intake negative pressure sensor.
 11. The intake negative pressuredetecting device for an internal combustion engine as set forth in claim3, wherein the intake pipe is formed so as to be curved into an arc-likeshape substantially about an imaginary point, and an opening of thecommunication passageway which is situated at an end portion on theintake passageway side is positioned in a portion on an innercircumferential surface of the intake passageway which is closer to theimaginary point at the downstream end of the intake passageway.
 12. Theintake negative pressure detecting device for an internal combustionengine as set forth in claim 10, wherein the intake pipe extends from aninternal combustion engine main body.
 13. The intake negative pressuredetecting device for an internal combustion engine as set forth in claim12, wherein the intake passageway is formed in the interior of theintake pipe and communicates with the intake passageway of the internalcombustion engine main body.
 14. The intake negative pressure detectingdevice for an internal combustion engine as set forth in claim 12,further comprising a fuel supply means for supplying fuel to theinternal combustion engine main body.
 15. The intake negative pressuredetecting device for an internal combustion engine as set forth in claim14, further comprising and a control unit that controls the supply offuel to the internal combustion engine main body by the fuel supplymeans based on a detection signal of the intake pressure sensor.
 16. Theintake negative pressure detecting device for an internal combustionengine as set forth in claim 1, wherein a cross-sectional area of adownstream side communication passageway which constitutes a portion ofthe communication passageway which is situated on the intake negativepressure sensor side thereof is made larger than a cross-sectional area(S1) of an upstream side communication passageway which constitutes aportion of the communication passageway which is situated on an intakepassageway side thereof.
 17. The intake negative pressure detectingdevice for an internal combustion engine as set forth in claim 16,wherein the intake negative pressure sensor includes a housing whichconstitutes an outer shell thereof and which is mounted on an exteriorside of the intake pipe.
 18. The intake negative pressure detectingdevice for an internal combustion engine as set forth in claim 17,wherein the intake negative pressure sensor includes a sensor main bodyaccommodated in an interior of the housing that detects an intakenegative pressure.
 19. The intake negative pressure detecting device foran internal combustion engine as set forth in claim 18, wherein theintake negative pressure sensor includes a pressure transmittingpassageway formed in the housing that transmits the intake negativepressure from the downstream side communication passageway to the sensormain body side.
 20. The intake negative pressure detecting device for aninternal combustion engine as set forth in claim 19, further comprisingan opening of the pressure transmitting passageway which opens to aninterior of the downstream side communication passageway deviated from acenter of an opening of the upstream side communication passageway whichopens to the interior of the downstream side communication passageway ina direction normal to the center.